"Micromachining" as the term is used herein, refers to a field of endeavor where extremely small (microscopic) mechanical devices are fabricated, often using semiconductor processing techniques, as on silicon dies. The techniques employed in the fabrication of these devices include those used to fabricate traditional semiconductor electronic devices--namely, deposition, doping, implantation, photolithography, etching, et cetera. However, the technologies employed to fabricate these devices has expanded from traditional semiconductor fabrication processes to more "conventional" techniques of cutting and grinding.
In some cases, mechanical and (as well as) electrical elements are fabricated on silicon to form a device such as a micromotor. In many cases, forming microscopic versions of mechanical devices poses some difficult problems in micromachining analogous devices on silicon. For example, making a rotor turn on a bearing is probably the most difficult task for a would-be micromechanic, since a theoretical understanding of friction on the microscale is lagging behind classical notions of friction on larger, more familiar scales.
There are already a number of mechanical "primitives" (for example wheels and levers) for micromachined devices. Among these are gears, rotors, levers and the like, useful in fabricating micromotors, microscopic tweezers, microprobes, micro-positioning arms, micro cantilevers, micro valves, micro bearings and bushings, cilia-like curling actuators, membranes, expanding/contracting parallelogram devices, and the like.
By and large, most micromachined devices are based on primitives that operate in the plane of the silicon substrate. Recently, however, primitives are being developed whose motion is perpendicular to the substrate. For example, actuators are being developed that curl up off the surface of a silicon die, and relax back onto the surface, akin to the motion of cilia. A purely upright element would evidently be useful for implementing grasping functions, akin to the movement of human fingers.
Generally, the field of micromachining is dominated by efforts to fabricate microscopic analogues of macroscopic devices and primitives in the medium of silicon. To some extent, this would appear to be antithetical to the generally accepted goal of replacing mechanical elements with electronic elements having fewer (perhaps none) moving parts.
There remains a need for additional micromachined devices, and primitives for such devices, which will expand the useful horizons of and applications for micromachining.